1. Field of the Invention
The present invention relates to thin walled containers for the storage of liquids. More particularly, this invention relates to blow molded, plastic containers capable of being filled with a liquid while the liquid is at a temperature elevated above the ambient temperature, configured to accommodate a partial vacuum formed within the container during cooling of the liquid after filling and capping, and configured to exhibit enhanced top load capabilities.
2. Description of the Prior Art
In the past, plastic containers have been used to contain liquids that were initially filled while chilled or at ambient temperatures. However, in recent years, plastic containers have been developed which can be used to contain liquids, such as processed fruit juices and the like, which are pasteurized and must be filled into the container while still hot and near pasteurized. Containers of this type are generally known as "hot-fill" containers and have become well known. Examples are shown in U.S. Pat. Nos. 4,805,788 and 4,863,046.
Hot-fill conditions impose mechanical stresses on the container structure which differ from those stresses imposed during non-hot-fill applications. These additional mechanical stresses cause the material forming the container to be less resistant to deformation when hot-filling both during and after. When subjected to the stresses of hot filing, conventional containers deform or collapse.
Additional concerns during hot-filling include a decrease in container rigidity, which occurs immediately after hot-filling, and reduced internal pressures which develop as the volume of the liquid in the container shrinks during cooling. Obviously, containers intended for hot-fill applications must be able to withstand both the initial decrease in rigidity and the subsequent decrease in internal pressures, while maintaining a desirable aesthetic appearance.
Various structural configurations and process methodologies have been developed to alleviate the above concerns. Most often, the material forming the container is heat treated or "heat set" to produce a container having better thermal stability. Heat setting of the container generally increases the crystallinity of the container, without adversely affecting the container appearance, and increases the strength and durability of the container. Additionally, hot-fill containers are generally provided with structural panels in the container side wall in order to fully accommodate volumetric shrinkages as the liquid cools. The vacuum panels themselves collapse or flex inwardly to accommodate the liquid as it shrinks in response to cooling. This inwardly flexing of the vacuum panels, however, creates additional undesirable stress points, particularly in the comers of the panels.
Containers of the above type have exhibited a limited ability to withstand top loading during filling, capping and stacking for transporting of the containers. Overcoming these problems is important because it would decrease the likelihood of a container's top or shoulder being crushed, as well as inhibiting ovalization in this area. Obviously, it is important to be able to stack containers so as to maximize the use of shipping space. It also enhances the ability to lightweight the container.
One way to eliminate the concerns related to the above mentioned stress points is to increase the thickness of the container's side wall. Such an increase also increases the material cost for the container and the weight of the container, both of which are unacceptable. Instead of increasing the side wall thickness, other solutions have included providing ribs extending along the edges of the panels, providing horizontal ribs in the panels themselves, providing smaller panels in multiple rows around the container, and by providing circumferential reinforcement ribs at the upper and lower edges of the panels. While all of the above methods have worked satisfactorily to some extent, none of these methods significantly increased the top loading capabilities.
As seen from the above discussion, the side wall of the container has been given considerable attention in the effort to control the mechanical stresses imposed on the container as a result of the hot-filling process. Little or no consideration has been given to the upper portion of the container, including the shoulder and waist regions of the container.
As mentioned above, a particular problem which can result from the hot-filling procedure is a decrease in the container's ability to withstand top loading during filling, capping and labeling. Because of the decreased container rigidity immediately after filling and after cooling, even heat set containers are less able to resist loads imparted through the top or upper portion of the container, such as when the containers are stacked one upon another for storage and shipping. Similar top loads are imparted to the container when it is dropped and lands on the upper portion or mouth of the container. As a result of this type of top loading, the container can become deformed and undesirable to the consumer.
In view of the foregoing limitations and shortcomings of the prior art containers, as well as other disadvantages not specifically mentioned above, it should be apparent that there exists a need for an improved hot-fill container having increased top loading capabilities.
Accordingly, it is an object of the present invention to fulfill that need by providing a hot-fill container having an increased top loading structural integrity.
It is also an object of this invention to provide a container having an upper portion which is reinforced by structural provisions that provide the container with an enhanced top loading capability.
Yet another object of the present invention is to provide a number of structural reinforcements in the waste region of the container to resist deformation of the container resulting from top loading.